In continuous ink jet printing, ink is supplied under pressure to a manifold region that distributes the ink to a plurality of orifices, typically arranged in a linear array(s). The ink discharges from the orifices in filaments which break into droplet streams. The approach for printing with these droplet streams is to selectively charge and deflect certain drops from their normal trajectories. Graphic reproduction is accomplished by selectively charging and deflecting drops from the drop streams and depositing at least some of the drops on a print receiving medium while other of the drops strike a drop catcher device. The continuous stream ink jet printing process is described, for example, in U.S. Pat. Nos. 4,255,754; 4,698,123 and 4,751,517, the disclosures of each of which are totally incorporated herein by reference.
In the ink jet printing art, water soluble dyes are desirable for runnability, but waterfast inks are highly desirable for producing permanent images. Decreasing the solubility of the dye increases the waterfastness, and vice versa. It is also known in the industry that a waterfast ink is highly desired for publishing and documentation, to prevent alteration of information on such documents.
One means for improving waterfastness is to use polymers and resins in inks to enhance adhesion of the dye to substrates. However, presence of resins in inks adversely affects machine runnability due to formation of deposits on orifice plates and charge plate buildup.
Ink jet ink compositions are known and generally contain water soluble dyes. Addition of polymeric additives to ink-jet inks, in order to improve permanency, is very well documented in the patent literature. For example, U.S. Pat. No. 5,244,496 teaches the addition of acrylic binder to the ink in order to achieve waterfastness and rub resistance. Another example is U.S. Pat. No. 5,254,158 where Example I described the use of polyethylene oxide/bisphenol polymer as an additive to the ink.
Addition of polymers and resins to inks has only a limited advantage in promoting dye fixation to the fiber. Unless the polymer is somehow attached to the dye molecule by chemical bonding, the polymer alone would cure on the paper leaving the soluble dye to bleed off the paper. In most cases when the interaction between the dye molecule and the polymer is left to some physical forces or weak hydrogen bonding, the waterfastness results are disappointing.
It is seen then that there is a need for improved waterfast dye for use in formulating ink jet permanent inks for ink jet recording equipment.